Electrostatic chucks, and/or susceptors, are employed to support a wafer, substrate or another type of workpiece during the manufacture of semiconductor devices. In one arrangement, wafers are secured to a chucking surface by an electrostatic force generated between an external electrode and an electrode embedded in a dielectric chuck body.
One method for fabricating electrostatic chucks having an embedded film electrode includes forming a first layer of a green ceramic material, screen printing a film electrode onto the first layer, depositing a second layer of the green ceramic material over the screen printed electrode and sintering the resulting preform.
Resulting chucks and/or susceptors, however, can display fluctuations or non-uniformities in the thickness of the dielectric layer above the electrode in spite of careful machining of the chucking surface. These fluctuations can adversely affect the operation of the chuck especially in the case of chucks for which the chucking force is inversely proportional to the square of the distance between the electrode and the workpiece.
Therefore, a need exists for electrostatic chucks or susceptors which have an embedded screen printed electrode and which display an uniform chucking force across their chucking surface.
It has been found that an electrostatic chuck having a flat screen printed electrode can be formed by screen printing the electrode upon a densified ceramic substrate, followed by depositing a green form of a ceramic layer onto and overlaying the electrode and by sintering the resulting structure.
The invention is directed to an electrostatic chuck. The electrostatic chuck of the invention includes a chuck body having a film electrode and a chucking surface. The film electrode is essentially flat and parallel to the chucking surface. In a preferred embodiment, the film electrode is screen printed.
The invention also is directed to a method of producing an electrostatic chuck. The method of the invention includes depositing a film electrode on a surface of a sintered substrate. The surface of the sintered substrate can be smoothed by machining. A green layer of a ceramic material is formed onto and overlays the film electrode. The resulting structure is heated, optionally under pressure, thereby sintering the green layer and producing the electrostatic chuck.
In one embodiment of the invention, the sintered substrate is formed by sintering a green form of a ceramic material, such as, for example, a compacted powder. In another embodiment, the green layer of a ceramic material includes a compacted powder. In still another embodiment the film electrode is produced by screen printing.
Suitable film electrodes include a metal, such as, for example, molybdenum (Mo), tungsten (W), or combinations thereof. Suitable substrates include a ceramic material such as aluminum nitride, (AlN), alumina (aluminum oxide or Al2O3) boron nitride (BN), silicon nitride (Si3N4), combinations thereof and other materials. Suitable ceramic layers can include AlN, Al2O3, BN, Si3N4, combinations thereof and other materials. In a preferred embodiment, the substrate and the dielectric layer are fabricated from the same material.
The invention has several advantages. For example, the method of the invention does not require embedding a bulk metal electrode such as a foil, mesh or plate but can employ a screen printed electrode. Screen printing is particularly advantageous over bulk metal in conjunction with bipolar electrodes. A common bipolar electrode configuration is one where the inner electrode is concentric with but separated from the outer electrode by a defined gap (dielectric). Since it is important to maintain the separation of the two electrodes for the proper functioning of the electrostatic chuck, the screen printing process and the resulting electrode allows for the accurate definition and achievement of a uniform dielectric gap in bipolar configurations as compared to bulk metal electrodes. A similar advantage exists for screen printed electrodes where electrostatic chucks are designed with multipolar electrode configurations, for example, six independent electrodes. The film electrode obtained by the method of the invention is flat and the electrostatic chuck of the invention has good chucking properties and can exert an uniform chucking force upon a workpiece during wafer manufacturing.